TWI790052B - Radio frequency switch - Google Patents

Abstract

A radio frequency (RF) switch includes a signal terminal, a reference voltage terminal, and a shunt switch path. The shunt switch path is coupled to the signal terminal and a reference voltage terminal, and includes a first shunt sub-path and a second shunt sub-path. When switched to a first state, the RF switch has a first resistance. When switched to a second state, the RF switch has a second resistance. When switched to a third state, the RF switch has a third resistance. The first resistance, the second resistance, and the third resistance are different from each other.

Description

RF switch

The invention relates to a radio frequency circuit, in particular to a radio frequency switch in the radio frequency circuit.

Radio Frequency (RF) switches can guide radio frequency signals through one or more transmission paths, and are widely used in televisions, mobile phones, wireless communication devices, wireless networks (Wi-Fi), Bluetooth and global positioning systems (global positioning system, GPS).

However, in the related art, when the RF switch is turned off, the RF signal will be reflected and the RF switch cannot work normally.

An embodiment of the present invention provides a radio frequency switch, including a signal terminal, a reference voltage terminal, and a shunt switch path, and the shunt switch path is coupled to the signal terminal and the reference voltage terminal. The shunt switch path includes a first shunt sub-circuit and a second shunt sub-circuit. The second shunt sub-circuit includes a first transistor and a second transistor connected in parallel. When the radio frequency switch is switched to a first state, it has a first impedance, when the radio frequency switch is switched to a second state, it has a second impedance, and when the radio frequency switch is switched to a third state, it has a third impedance. The first impedance, the second impedance, and the third impedance are different.

1 to 7: RF switch

10,18,181,182: signal terminal

12,22,32,221,222: shunt switch path

14,16,26,261,141,262,142: shunt sub-circuit

40, 401, 402: Series switch paths

42: Antenna

44: RF circuit

GND: reference voltage terminal

Srf: radio frequency signal

Tsh, T1, T2, Tsr: Transistor

Rsh, Rsr, R1, R2: resistance

Vcsh, Vc1, Vc2, Vsr, Vc11, Vc21, Vcsh1, Vcsr1, Vc12, Vc22, Vcsh2, Vcsr2: control voltage

Figure 1 is a schematic circuit diagram of a radio frequency switch in an embodiment of the present invention.

Figure 2 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 3 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 4 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 5 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 6 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 7 is a schematic circuit diagram of another radio frequency switch in the embodiment of the present invention.

Fig. 1 is a schematic circuit diagram of a radio frequency switch 1 in an embodiment of the present invention. The radio frequency switch 1 can transmit or receive radio frequency signal Srf.

The RF switch 1 includes a signal terminal 10 , a reference voltage terminal GND, a shunt switch path 12 , and a signal terminal 18 . The shunt switch path 12 is coupled to the signal terminal 10 and the reference voltage terminal GND. The signal terminal 10 can be coupled to one of the antenna and the radio frequency circuit, and the signal terminal 18 can be coupled to the other of the antenna and the radio frequency circuit. The reference voltage terminal GND can provide a reference voltage, such as 0V. When the RF switch 1 is turned on, the shunt switch path 12 is turned off, and the shunt switch path 12 can cut off the coupling between the signal terminal 10 and the reference voltage terminal GND to transmit the radio frequency signal Srf between the signal terminal 10 and the signal terminal 18 ; When the RF switch 1 is turned off, the shunt switch path 12 is turned on, and the shunt switch path 12 can establish a coupling between the signal terminal 10 and the reference voltage terminal GND to guide the radio frequency signal Srf to the reference voltage terminal GND. The radio frequency switch 1 of the present invention can selectively provide an equivalent resistance substantially equal to the load resistance in a corresponding state. The load resistance can be an equivalent resistance of the antenna and the radio frequency circuit, such as 50 ohms or 75 ohms.

The shunt switch path 12 includes a shunt sub-circuit 14 and a shunt sub-circuit 16 . The shunt sub-circuit 14 includes a first end coupled to the signal end 10 and the signal end 18, a second end, and a control end for receiving control The control voltage Vcsh is used to control the shunt sub-circuit 14 . The shunt sub-circuit 16 includes a first end coupled to the second end of the shunt sub-circuit 14 , and the second end is coupled to the reference voltage terminal GND. The shunt sub-circuit 14 may include N stacked transistors Tsh, where N is a positive integer. The size of each transistor Tsh can be equal, and its conduction state can be controlled by the control voltage Vcsh. The number N of transistors Tsh in the shunt sub-circuit 14 can be determined by the power of the radio frequency signal Srf. For example, the greater the power of the radio frequency signal Srf, the more transistors Tsh need to be configured in the shunt sub-circuit 14 to provide sufficient isolation capability when transmitting or receiving the radio frequency signal Srf. In some embodiments, the number N of transistors Tsh may be 24. The shunt sub-circuit 14 may further include N resistors Rsh, each resistor Rsh is coupled to the first terminal and the second terminal of the corresponding cascade transistor Tsh, and the resistance value of each resistor Rsh may be equal. When the shunt switch path 12 is cut off, all the N stacked transistors Tsh are cut off, and each transistor Tsh can be equivalent to a capacitor. When the shunt switch path 12 is turned on, the N stacked transistors Tsh are all turned on. At this time, each transistor Tsh is electrically equivalent to a resistance when it is turned on. The value of this resistance is very small and approaches 0 ohms, 24 When a transistor Tsh is turned on, it can be equal to 48 ohms, and at this time, the shunt switch path 12 can be equivalent to a resistance of 50 ohms. For example, the resistor Rsh can be used as a bias resistor to fix the potentials of the first terminal and the second terminal of the transistor Tsh when the shunt switch path 12 is turned on, and the resistance value of the resistor Rsh can be between 10K ohms and 50K ohms. In some embodiments, the impedance of the equivalent capacitance of the shunt sub-circuit 14 when the transistor Tsh is turned off is much smaller than the impedance of the resistor Rsh by selecting the resistor Rsh.

The shunt sub-circuit 16 includes a transistor T1 and a transistor T2 connected in parallel. The transistor T1 may include a first end coupled to the first end of the shunt sub-circuit 16, a second end coupled to the second end of the shunt sub-circuit 16, and a control end used for The control voltage Vc1 is received to control the conduction state of the transistor T1. The transistor T2 may include a first end coupled to the first end of the shunt sub-circuit 16, a second end coupled to the second end of the shunt sub-circuit 16, and a control end for receiving The control voltage Vc2 is used to control the conduction state of the transistor T2. The size of the transistor T1, the size of the transistor T2 and the size of the transistor Tsh can be different. For example, in some embodiments, the size of transistor Tsh may be larger than transistor Tsh The size of the body T1, and the size of the transistor T1 can be larger than the size of the transistor T2. In some embodiments, the size of the transistor Tsh may be equal to the sum of the size of the transistor T1 and the size of the transistor T2. In some embodiments, the size of the transistor T2 can be selected such that when the transistor T2 is turned on, the equivalent resistance of the shunt switch path 12 approaches the on-resistance of the load resistor. For example, the on-resistance of the transistor T2 can be selected to be between 30 ohms and 48 ohms, so that the equivalent resistance of the shunt switch path 12 at this time is approximately equal to 50 ohms. In some embodiments, the size ratio of the transistor T1 and the transistor T2 may be between 70:30 and 99:1. For example, the size ratio of transistor Tsh, transistor T1 and transistor T2 may be 100:99:1. Since the size of the transistor Tsh and the size of the transistor T1 are much larger than the size of the transistor T2 at this time, when the transistor Tsh or the transistor T1 is turned on, it can be regarded as a short circuit. In some embodiments, when the shunt switch path 12 is turned on, the radio frequency signal Srf can be guided to the reference voltage terminal GND through 24 transistors Tsh (0 ohm) and transistor T2 (50 ohm), so no signal will be generated Reflection degrades signal quality. In some other embodiments, when the shunt switch path 12 is turned on, the radio frequency signal Srf can be guided to the reference voltage terminal GND through 24 transistors Tsh (0 ohm) and transistor T1 (0 ohm). The transistor Tsh, the transistor T1 and the transistor T2 can all be N-type metal-oxide-semiconductor field-effect transistors (MOSFETs).

In some embodiments, the size of the transistors Tsh, T1, and T2 may be directly related to the finger width of each transistor Tsh, T1, and T2, respectively. For example, in an embodiment where the size ratio of transistor Tsh, transistor T1 and transistor T2 is 100:99:1, the knuckle width of transistor Tsh can be 10 microns, the number of knuckles is 100, and transistor T1 The knuckle width of T2 may be 9.9 microns and the number of knuckles is 100, and the knuckle width of transistor T2 may be 0.1 microns and the number of knuckles is 100. Therefore, the size of transistor Tsh may be 10 microns*100 knuckles, the size of transistor T1 may be 9.9 microns*100 knuckles, and the size of transistor T2 may be 0.1 microns*100 knuckles. In some other embodiments, the size of transistors Tsh, T1, and T2 can be directly related to the number of fingers of each transistor Tsh, T1, and T2, so as to provide simple circuit layout and better static Electrostatic discharge (ESD) characteristics. For example, transistor Tsh has a knuckle width of 10 microns and a knuckle count of 100 knuckles, transistor T1 has a knuckle width of 10 microns and a knuckle count of 99 knuckles, and transistor T2 has a knuckle width of 10 micron, the number of knuckles is 1 knuckle. Therefore, the size of transistor Tsh may be 10 microns*100 knuckles, the size of transistor T1 may be 10 microns*99 knuckles, and the size of transistor T2 may be 10 microns*1 knuckle.

The radio frequency switch 1 can be switched to one of the states S0 to S3, as shown in Table 1:

As shown in Table 1, when the RF switch 1 is switched to the state S0, the shunt sub-circuit 14 receives -2.5V to be turned off, and the transistor T1 and the transistor T2 also receive 2.5V to be turned on, so that the RF switch 1 has Impedance Z0, which may be equal to 1/jw(Coff/N), where Coff is the equivalent capacitance value of each transistor Tsh when it is off, and N is the number of transistors Tsh. When the radio frequency switch 1 is switched to the state S1, the shunt sub-circuit 14 receives -2.5V to be cut off, and the transistor T1 and the transistor T2 also receive -2.5V to be cut off, so that the radio frequency switch 1 has an impedance Z1, which can It is equal to 1/jw(Coff/(N+1)). When the RF switch 1 switches to the state S2, the shunt sub-circuit 14 receives 2.5V to be turned on, and the transistor T1 and the transistor T2 receive 2.5V to be turned on, so that the RF switch 1 has an impedance Z2, which can be equal to 0 ohms . When the RF switch 1 switches to the state S3, the shunt sub-circuit 14 receives 2.5V to be turned on, the transistor T1 receives -2.5V to be turned off, and the transistor T2 receives 2.5V to be turned on, The RF switch 1 has an impedance Z3 which can be equal to 50 ohms, that is, the impedances Z0 to Z3 are all different, and one of them can be equal to 50 ohms. Impedance Z3 can be matched to the load resistance. For example, impedance Z3 may be close to 50 ohms or 75 ohms. Impedance Z1 may be greater than impedance Z3, and impedance Z3 may be greater than impedance Z2. The states S0 and S1 are applicable when the radio frequency switch 1 is turned on, and the states S2 and S3 are applicable when the radio frequency switch 1 is turned off. When the RF switch 1 is switched to the state S3 to be cut off, since the RF signal Srf is guided to the reference voltage terminal GND through the impedance Z3 matched with the load resistance, no signal reflection will occur to degrade the signal quality.

Although Table 1 shows that -2.5V is used to cut off the shunt sub-circuit 14, transistor T1, and/or transistor T2, those skilled in the art will know that other voltages less than -2.5V can be used to cut off the shunt sub-circuit 14, transistor T1. , and/or transistor T2. In addition, although Table 1 shows that 2.5V is used to turn on the shunt sub-circuit 14, transistor T1, and/or transistor T2, those skilled in the art will know that other than transistor Tsh, transistor T1, and/or transistor T2 can be used. The voltage corresponding to the threshold voltage turns on the shunt sub-circuit 14, the transistor T1, and/or the transistor T2. In some embodiments, the transistors T1 , T2 can also generate impedances in states S0 to S3 by changing the control voltages Vc1 , Vc2 .

The radio frequency switch 1 can provide an equivalent resistance substantially equal to the load resistance when it is turned on or off, so as to improve the signal quality without increasing the circuit area.

Fig. 2 is a schematic circuit diagram of another radio frequency switch 2 in the embodiment of the present invention. The difference between the RF switch 2 and the RF switch 1 is that the transistor T1 and the transistor T2 of the shunt sub-circuit 26 of the shunt switch path 22 are respectively connected in parallel with a resistor R1 and a resistor R2 . When the shunt switch path 22 is cut off, the resistor 1 can be used as a bias resistor to fix the potentials of the first terminal and the second terminal of the transistor T1, and the resistor 2 can be used as a bias resistor to fix the first terminal and the second terminal of the transistor T2. terminal potential. The operation mode of the radio frequency switch 2 is similar to that of the radio frequency switch 1 and will not be repeated here.

Fig. 3 is a schematic circuit diagram of another radio frequency switch 3 in the embodiment of the present invention. The difference between the RF switch 3 and the RF switch 1 lies in that the shunt sub-circuit 14 and the shunt sub-circuit 16 of the shunt switch path 32 are exchanged. The first end of the shunt sub-circuit 16 is coupled to the signal end 10 and the signal end 18 . The first end of the shunt sub-circuit 14 is coupled to the second end of the shunt sub-circuit 16 , and the second end of the shunt sub-circuit 14 is coupled to the reference voltage terminal GND. The operation mode of the radio frequency switch 3 is similar to that of the radio frequency switch 1 and will not be repeated here.

FIG. 4 is a schematic circuit diagram of another radio frequency switch 4 in the embodiment of the present invention. The difference between the RF switch 4 and the RF switch 2 is that the RF switch 4 further includes a series switch path 40 . The series switch path 40 includes a first end coupled to the signal end 10 , and a second end coupled to the signal end 18 . The signal terminal 10 is coupled to the antenna 42 , and the signal terminal 18 is coupled to the radio frequency circuit 44 . The radio frequency circuit 44 can be a matching circuit, a power amplifier, or other circuits. When the series switch path 40 is turned on, the series switch path 40 can establish a coupling between the signal terminal 10 and the signal terminal 18 to transmit the radio frequency signal Srf between the signal terminal 10 and the signal terminal 18; when the series switch path 40 is turned off , the series switch path 40 can cut off the coupling between the signal terminal 10 and the signal terminal 18 to prohibit the transmission of the radio frequency signal Srf between the signal terminal 10 and the signal terminal 18 . The equivalent resistance of the antenna 42 and the equivalent resistance of the radio frequency circuit 44 may be substantially equal. The series switch path 40 may include a transistor Tsr and a resistor Rsr connected in parallel. The transistor Tsr includes a first terminal coupled to the signal terminal 10 , a second terminal coupled to the shunt switch path 22 and the signal terminal 18 , and a control terminal for receiving the control voltage Vcsr to control the transistor Tsr. The resistor Rsh includes a first terminal coupled to the first terminal of the transistor Tsr, and a second terminal coupled to the second terminal of the transistor Tsr. The transistor Tsr can be an N-type MOSFET. Although FIG. 4 shows that the series switch path 40 only includes one transistor Tsr and one resistor Rsr, in other embodiments, the series switch path 40 may also include M transistors Tsr and M resistors Rsr, M transistors The Tsr are stacked sequentially, and each resistor Rsr is coupled to the first end and the second end of the corresponding stacked transistor Tsr, and M is a positive integer. The operation mode of the radio frequency switch 4 is similar to that of the radio frequency switch 2 and will not be repeated here.

Fig. 5 is a schematic circuit diagram of another radio frequency switch 5 in the embodiment of the present invention. The difference between the RF switch 5 and the RF switch 4 is that the first end of the series switch path 40 is coupled to the signal end 18 , and the second end of the series switch path 40 is coupled to the signal end 10 . The operation mode of the radio frequency switch 5 is similar to that of the radio frequency switch 4 and will not be repeated here.

Fig. 6 is a schematic circuit diagram of another radio frequency switch 6 in the embodiment of the present invention. The RF switch 6 is a single-pole double-throw (SPDT) switch. The difference between the RF switch 6 and the RF switch 4 is that the RF switch 6 includes series switch paths 401 and 402 , shunt switch paths 221 and 222 , and signal terminals 181 and 182 . The circuit arrangement and operation method of the series switch paths 401 and 402 are similar to the series switch path 40 , and the circuit arrangement and operation method of the shunt switch paths 221 and 222 are similar to the shunt switch path 22 , which will not be repeated here. The radio frequency switch 6 can receive the control voltages Vc11, Vc21, Vcsh1, Vcsr1, Vc12, Vc22, Vcsh2, Vcsr2 to form a path between the signal terminal 10 and one of the signal terminals 181 and 182 to transmit or receive the radio frequency signal Srf. When the RF switch 6 forms a path between the signal terminal 10 and the signal terminal 181 , the series switch path 401 is turned on, the shunt switch path 221 is turned off, the series switch path 402 is turned off, and the shunt switch path 222 is turned on. When the RF switch 6 forms a path between the signal terminal 10 and the signal terminal 182 , the series switch path 401 is turned off, the shunt switch path 221 is turned on, the series switch path 402 is turned on, and the shunt switch path 222 is turned off.

Fig. 7 is a schematic circuit diagram of another radio frequency switch 7 in the embodiment of the present invention. The difference between the RF switch 7 and the RF switch 5 is that the RF switch 7 includes series switch paths 401 and 402 and signal terminals 181 and 182 . The circuit configuration and operation of the series switch paths 401 and 402 are similar to those of the series switch path 40 , and will not be repeated here. The radio frequency switch 7 can receive control voltages Vc1, Vc2, Vcsh, Vcsr1, Vcsr2 to form a path between the signal terminal 10 and one of the signal terminals 181 and 182 to transmit or receive radio frequency signals Srf, or disable the radio frequency switch 7 to interrupt the coupling between the signal terminal 10 and the signal terminal 181 , and to interrupt the coupling between the signal terminal 10 and the signal terminal 182 . When the RF switch 7 forms a path between the signal terminal 10 and the signal terminal 181 , the series switch path 401 is turned on, the series switch path 402 is turned off, and the shunt switch path 22 is turned off. When the RF switch 7 forms a path between the signal terminal 10 and the signal terminal 182 , the series switch path 401 is turned off, the series switch path 402 is turned on, and the shunt switch path 22 is turned off. When the RF switch 7 is disabled, the series switch path 401 is turned off, the series switch path 402 is turned off, and the shunt switch path 22 is turned on.

The RF switches 1 to 7 can provide an equivalent resistance substantially equal to the load resistance when they are turned on or off, so as to improve the signal quality without increasing the circuit area. The above descriptions are only preferred embodiments of the present invention, and all equivalent changes and modifications made according to the scope of the patent application of the present invention shall fall within the scope of the present invention.

1: RF switch

10,18: signal terminal

12: Shunt switch path

14,16: shunt sub-circuit

GND: reference voltage terminal

Srf: radio frequency signal

Tsh, T1, T2: Transistor

Rsh: resistance

Vcsh, Vc1, Vc2: control voltage

Claims (20)

A radio frequency switch, which includes: a signal terminal; a reference voltage terminal; and a shunt switch path, coupled to the signal end and the reference voltage end, the shunt switch path includes: a first shunt sub-circuit; and A second shunt sub-circuit, comprising a first transistor and a second transistor connected in parallel; wherein when the radio frequency switch is switched to a first state, it has a first impedance, when the radio frequency switch is switched to a In the second state, it has a second impedance, when the radio frequency switch switches to a third state, it has a third impedance; and the first impedance, the second impedance, and the third impedance are different. The radio frequency switch according to claim 1, wherein the first shunt sub-circuit includes a plurality of stacked transistors. The radio frequency switch as claimed in claim 2, wherein a size of the plurality of stacked transistors, a size of the first transistor, and a size of the second transistor are different. The radio frequency switch as claimed in claim 3, wherein the size of the plurality of stacked transistors is larger than the size of the first transistor, and the size of the first transistor is larger than the size of the second transistor. The radio frequency switch as claimed in item 3, wherein the size of the plurality of stacked transistors equal to the sum of the size of the first transistor and the size of the second transistor. The radio frequency switch as described in claim 2, wherein the first shunt sub-circuit further includes a plurality of resistors, each resistor is coupled to a first end of a corresponding stacked transistor in the plurality of stacked transistors and a second end. The radio frequency switch as claimed in claim 1, wherein a size of the first transistor and a size of the second transistor are different. The radio frequency switch as claimed in claim 7, wherein the size of the first transistor is larger than the size of the second transistor. The radio frequency switch according to claim 1, wherein a size ratio of the first transistor and the second transistor is 99:1. The radio frequency switch as claimed in claim 1, wherein when the second transistor is turned on, it has an on-resistance, and the on-resistance approaches a load resistance. The radio frequency switch as claimed in claim 10, wherein the on-resistance is equal to 50 ohms. The radio frequency switch as claimed in claim 1, wherein one of the first impedance, the second impedance, and the third impedance is equal to 50 ohms. The radio frequency switch as claimed in claim 1, wherein the third impedance matches a load resistance. The radio frequency switch according to claim 1, wherein the third impedance is close to 50 ohms or 75 ohms. The radio frequency switch as described in Claim 1 further includes a series switch path coupled to the signal terminal and a radio frequency circuit. The radio frequency switch as claimed in claim 1, wherein the signal terminal is coupled to an antenna. The radio frequency switch according to claim 1, wherein when the radio frequency switch is switched to the first state, the first shunt sub-circuit is turned off, and the first transistor and the second transistor are turned off. The radio frequency switch according to claim 1, wherein when the radio frequency switch is switched to the second state, the first shunt sub-circuit is turned on, and the first transistor and the second transistor are turned on. The radio frequency switch according to claim 1, wherein when the radio frequency switch is switched to the third state, the first shunt sub-circuit is turned on, the first transistor is turned off, and the second transistor is turned on. The radio frequency switch according to claim 1, wherein the first impedance is greater than the third impedance, and the third impedance is greater than the second impedance.

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